Without limiting the scope of the present invention, its background will be described in relation to forming a window in a casing string for a multilateral well, as an example.
In multilateral wells it is common practice to drill a branch or lateral wellbore extending laterally from an intersection with a main or parent wellbore. Typically, once the casing string is installed and the parent wellbore has been completed, a whipstock is positioned in the casing string at the desired intersection and then a rotating mill is deflected laterally off of the whipstock to form a window through the casing sidewall.
Once the casing window is created, the lateral wellbore can drilled. In certain lateral wellbores, when the drilling operation has been completed, a casing string is installed in the lateral branch. Casing the lateral branch may be accomplished with the installation of a liner string that is supported in the main wellbore and extends a desired distance into the lateral wellbore. Once the lateral casing string is installed and the lateral wellbore has been completed, it may be desirable to reestablish access to the main wellbore. In such cases, a rotating mill may be use to form an access window through the lateral casing sidewall.
It has been found, however, that the milling process used to form the lateral window and the main wellbore access window usually produces a large amount of debris, such as small pieces of the metal casing, which accumulate in the parent wellbore. This debris may make the whipstock difficult to retrieve after the milling process is completed. In addition, even after the whipstock is retrieved, the debris may cause other problems, such as plugging flow control devices, damaging seals, obstructing seal bores, interfering with passage of equipment past the intersection and the like.
Accordingly, a need has arisen for an improved system and method of opening windows in the casing strings during multilateral wellbore construction. In addition, a need has arisen for such an improved system and method that does not require the use of a mill that generates wellbore debris during multilateral wellbore construction.